Sludge handling method and apparatus



Sept. 13, 1949 c. YEOMANS SLUDGE HANDLING METHOD AND APPARATUS Filed March 19, 1945 mmkwmmio mommwmm 2 OU umTEosTAT Patented Sept. 13, 1949 i SLUDGE HANDLING METHOD AND APPARATUS Charles Yeomans, Hubbard Woods, 111., assignor to Yeomans Brothers Company, Chicago, Ill., a corporation of Delaware 7 Application March 19, mistrial No. 583,539

' 6 Claims.

This invention relates to an improvement in apparatus for pumping sludge from a sewage settling tank to a digester, in which the sludge is decomposed to form a combustible gas which is stored under pressure and delivered to various gas burning appliances.

One of the difficult problems in moving sludge from the bottom of a settling tank to a digester, is that of maintaining a pump in efi cient operating condition. Reciprocating pumps have generally been used for the purpose of transferring the sludge from the settling tank to the digester, and these pumps require frequent cleaning and reseating of valves in order that they may operate efliciently. This is, of course, due to the character of material handled. Such cleaning is not only an expensive, time-consuming operation, but it is also objectionable because it subjects the workmen who do the cleaning to the dangers of serious infection and illness or asphyxiation due to back flow of gas from the digester. There is also the danger of producing an explosive mixture of gas and air incident to the escape of some of the gas. Again, continuity of operation requires the costly provision of alternate pumping equipment, each unit of which may be placed in operation when the other is taken down for cleaning and adjustment.

It has heretofore been proposed to employ pneumatic, or gas displacement type, ejectors for this purpose but their use has not met with general acceptance because of some possibility that air from the pneumatic ejecting equipment will become mixed with the gas produced in the digester to form a highly explosive gas mixture.

'The main object of the present invention is to provide an arrangement whereby an ejector similar to a pneumatic ejector, may be employed for moving sludge from a settling tank to a digester without incurring any risk of producing an explosive mixture of air and gas.

Another object of the invention is to provide ejector equipment of the character indicated, which may be employed without incurring any danger from the escape of gas produced in the digester, which gas is highly poisonous. Still another object of the invention is to provide a sludge moving system which will be automatically operative for an extended, if not indefinite, period of time without maintenance or other servicing, and which will for these and other reasons be'exceptionally' low in cost of maintenance and operation.

Other objects and, advantages of the invention .will be understoodby reference t the following specificationand accompanying drawing wherein there is diagrammatically illustrated the improved method and apparatus. 7 i

In the drawing, I v

Fig; l is a diagrammatic illustration of the system and apparatus, and H Fig. 2 is an enlarged detail sectional view.

In connection with most sewage treatment plants, there is provided a settling tank or basin I which is equippedne ar its top with a peripheral trough forming weir 2. The heavy solid particles "of sewage delivered into the basin settle to thebottom of the basin while the supernatant liquid flows over the upper edge of the weir 2 v into the trough from which it is'in turn conductedto other clarifying treatments or to apoint of disposal.

Sludge is drawn from the bottom portion of the tank by an outlet, pipe 3 which preferably extends from near the bottom of the settling basin'to near the top thereof as shown, the outlet portion of the pipe 3 being, in conventional practice, connected to the suction side of a pump which discharges the sludge through a suitable pipeline into a digester In the digester, the sludge is decomposed and a combustible gas {methane) is formed which is drawn off by a compressor 5 which delivers the gas under suitable pressure, for example, 30 pounds per square inch, to a suitable gas holder 6. From the gas holder 6, the gas is conducted through a pipeline I to various appliances wherein the gas is used.

According to the present invention, the sludge is conducted from the settling tank I into a receiveril. The sludge enters the receiver through the inlet pipe 9 communicatin with the bottom of the receiver and it is discharged from the receiver through a discharge pipe it! which communicates through apipeline H with the digester 4. Suitable check valves indicated at l2 and I3 are provided in the intake and discharge pipelines of the receiver 8 to prevent reverse flow of the sludge. Also, suitable valves, such as indicated at M and i5 respectively, are provided in said pipelines for permitting closing thereof.

The receiver 8 has a top opening closed by a cover l6 which is equipped with a suitable stuffmg box I! through which there is slidably mounted a shaft or rod l8. The lower end of the rod l8 has connected to it downwardly and upwardly facing bells l9 and 20 respectively, the

samebeing spaced about as shown in the drawing, andso arranged that the weight of liquid a 3 in the lower bell will always tend to move the rod downwardly into the receiver whil air trapped in the downwardly facing bell l9 when the sludge level reaches the lower edge of the bell, will operate to lift the bell and move the rod I8 upwardly through said stufling box.

The upper end of the rod [8 is connected by means of a link 2| to the arm 22 of a bell crank lever, the other arm 23 of which is connected to the piston 24 of a 3-way valve 25. The valve 25 has one port 26 in communication with the in-.

terior of the receiver 8, another port 2'! connected by means of a pipeline .28 to the gas holder 6, and another port 29 connected by means of a pipeline 3%] to the digester 4.

When the sewage level in the receiver reaches a predetermined high point, the piston 2401': the valve 25 will be moved from the position shown to the right hand side of the valve so as to establish communication between the valve ports 21 and 26 and to close communication between the valve ports 26 and '29. When the valve is shifted to that position, gas under pressure from the gas holder 6 will flow through the pipeline 28, through the valve and into the upper portion of the receiver 8. Said gas being under pressure as aforesaid, will .force the sludge downwardly in the receiver and out through the discharge pipe l0 and through the pipeline ll into the digester. When the sludge level is lowered sufficiently, the weight of liquid in the bell 20 will restore the valve plunger 24 to the position shown, wherein communication between the valve ports 26 and 21 is closed and communication between the valve ports 2'6 and '29 established. The gas trapped under pressure in the pump part of the receiver 8 will then be permitted to escape through the valve and the pipeline 30 into the digester. The gas accumulatedin the digester'4 will generally be under a slight pressure (about 8 inches of water) but that pressure may readily be overcome by so arranging the receiver relative to the settling tank that there is a counteracting or equivalent sludge column in the pipeline leading from the settling tank to the receiver. Hence, the gas pressure in the digester need not interfere with they free exhaust of gas from the receiver to the digester when the valve is adjusted to the position shown in the drawing. Accordingly the operation of filling a receiver and discharging it will be repeated from time to time, the operation being completely automatic and requiring no attention.

By employing the pressure gas from the gas holder for ejecting sludge from the receiver, there is of course no danger of creating an explosive air and gas mixture. Also, the arrangement involves no loss of gas since all of the gas used for expelling the sludge from the receiver 8 is retained in the system by being returned to the digester from which it' again flows through the compressor into the gas holder.

It is desirable that the rod I8 be vertically movable without excessive bindin by the stufling box which must be provided to prevent leakage of gas from the receiver around the rod l8.

To prevent the escape of gas without'necessitating excessive tightening of the packing 3| around the rod l8, the stuffing box arrangement shown in Fig. 2 is provided. As there'shown, the packing gland 32 is provided with a groove or chamber 33 around the rod 18 and near the upper end of the gland. Said chamber 33 communicates through a port 34 with a relief pipe 35, which is preferably vented to the atmosphere where it will offer no danger to life. The small quantity of leakage gas vented to the atmosphere would be negligible so far as health and safety factors are concerned.

Above the chamber 33, the gland is provided with an auxiliary packing filled recess 36, which is closed by a pressure plate 31. The auxiliary packing in the recess 36 will, of course, be sufficiently tight around the rod I 8 to prevent the passage of any gas from the chamber 33 upwardly around the rod. The amount of packing in the chamber 33 will be small as compared with the amount of the packing 3I' so that said auxiliary packing will not alTord any objectionable grip on the rod IB to interfere with its vertical movement.

Means other than the described vertically movable bell arrangement may be employed for controlling the admission and relief of gas to and from the receiver. Such other means are well known in the art. The described arrangement is intended only to represent a typical control means and it may be replaced by any of the well known alternatives which serve or are adaptable to the same purpose. Also, sewage and materials other than sludge may be moved by the described apparatus, and the term, sludge is used in the following claims merely to refer to the material moved rather than to limit the scope of the invention to the moving of that particular material.

I claim:

1. In a treating system of the class described wherein material is delivered to a digester, in which a combustible gas "is formed, and wherein such gas is'compressed by a compressor and delivered to a gas holder for delivery to gas using appliances, the method of moving material into the digester which consists in delivering the material to be moved to the receiver of a gas displacement ejector, admitting compressed gas from the gas holder to said ejector receiver to effect movement of material from the ejector into the digester, and finally venting the ejector by returning the gas supplied thereto to said digester without substantial loss and without substantial dilution thereof.

2. In a sewage treating system wherein sludge is settled out in a settling tank and delivered to a digester, in which a combustible gas is formed, and wherein such gas is compressed by a compressor and delivered to a gas holder for delivery to gas using appliances, the method of moving sludge from the settling tank to the digester which consists in delivering the sludge to be moved to the receiver of a gas displacement ejector by gravity flow from the settling tank to the receiver, admitting gas under pressure from said gas holder to said receiver to effect movement of sludge from the receiver into the digester, and finally venting the ejector receiver by returning the gas supplied thereto to said digester without substantial loss and without substantial dilution thereof.

3. In a sewage treating system wherein sludge is settled out in a settling tank and delivered to a digester in which a combustible gas is formed, and wherein such gas is compressed by a'compressor and delivered to a gas holder, the method of moving sludge from the settling tank to the digester which consists in delivering the sludge to be moved to the receiver of a gas displacement termined level, said gas under pressure serving to effect movement of the sludge from the receiver through said outlet opening and into the digester, and finally venting the ejector receiver, by returning the gas supplied thereto to said digester without substantial loss and without substantial dilution thereof, when the level of sludge in the receiver reaches a predetermined low level, thereby to permit sludge to again flow into the receiver.

4. In apparatus of the class described, a digester, means for collecting and holding under pressure the gas produced in said digester, said means including a gas holder, piping, and a compressor which is connected to said gas holder and to said digest-er by said piping and which is operable to withdraw gas from said digester and to deliver said gas under pressure to said gas holder, a gas displacement ejector which includes a receiver having inlet and outlet connections, means operable to cause the material to be moved by said ejector to flow into said receiver through said inlet connection, piping connecting said outlet connection with said dig'ester, valve means for preventing reverse flow through the inlet and outlet connections to said receiver, a three-way, ejector-control valve, piping connecting one port of said three-way valve to said digester, another port to said gas holder, and the third port to said receiver, means responsive to the level of the material in said receiver for actuating said threeway valve to effect the flow of gas under pressure from said holder to said receiver when the level of the material in the receiver reaches a prede- -termined level, thereby to effect movement of material from said receiver to said digester, said level responsive means being also operative to actuate said three-way valve when the level of the material in said receiver reaches a predetermined low-er level to vent said ejector and to efiect the return of the pressure gas supplied from said holder to said digester without substantial loss and without substantial dilution thereof.

5. In apparatus of the class described, the combination of a settling tank, a digester, means for collecting and for holding under pressure the gas produced in said digester, said means including a gas holder, piping, and a compressor which is connected to said gas holder and to said digester by said piping and which is operable to deliver said gas under pressure to said gas holder, a gas displacement ejector which includes a receiver, a pipeline connecting said settling tank with said receiver, means operable to cause material which settles out in said settling tank to flow through said pipeline into said receiver, a second pipeline connecting said receiver with said digester for the transmission of material from said receiver to said digester, valve means for preventing reverse flow in said pipelines, a three-way valve having one port connected to said digester, another port connected to said gas holder, and the third port connected to said receiver, means responsive to the level of material in said receiver for actuating said three-way valve so as to cause gas under pressure to flow from said gas holder into said receiver when the level of the material in said receiver reaches a predetermined level, said level responsive means being also operative to actuate said valve to establish communication between the upper portion of said receiver and said digester when the level of the material in said receiver reaches a predetermined lower level, thereby venting said receiver and causing the pressure gas so vented to be returned to said digester.

6. Apparatus according to claim 5 wherein said level responsive, valve actuating means comprises a rod movable inwardly and outwardly through a portion of said receiver, a stufii-ng box disposed around said rod for preventing the escape of gas around said rod from said receiver, said stuffing box including a gland having an annular recess surrounding said rod and a port, extending from said annular recess, for venting the gas collected in said recess, and an auxiliary stufling box in said gland above said recess.

CHARLES YEOMANS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 724,051 Scholl Mar. 31, 1903 948,725 Freeman Feb. 8, 1910 1,008,884 Anderson Nov. 14, 1911 1,247,540 Jones Nov. 20, 1917 1,420,250 Gavett June 20, 1922 1,757,262 Sims May 6, 1930 2,097,454 Fischer Nov. 2, 1937 2,190,598 Fischer Feb. 13, 1940 2,280,930 Reeves Apr. 28, 1942 2,348,670 Woodward May 9, 1944 2,383,834 Yeomans Aug. 28, 1945 

